Functionality should be right on top of your priorities. Don’t let the seller show you – insist on trying it out yourself.
-Systematically test every button on the topside control, one at a time, checking to make sure that each is accurately labeled.
-Make sure every button feels right and properly activates what it should.
-Turn every dial/knob along the perimeter, once with pump(s) off (under no pressure), then again with the pump(s) on high to make sure they work properly and don’t leak.